Rechargeable lithium ion batteries have been the major power sources for a wide range of electronic products since their first commercialization in the 1990s. At present, they are being considered to power electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVS) to alleviate the increasing energy crisis and air pollution. For such applications, lithium ion batteries providing higher energy density and higher power capability are required to meet the energy and power demands of such vehicles.
To prepare lithium ion cells with an increased practical energy density, cathodic materials having high specific capacity, high operating voltage, high packing density, and good rate capability are desired. To obtain a higher rate capability, and thus a higher power capability, both good ionic conductivity with rapid lithium-ion diffusion within the host, and good electronic conductivity, to transfer electrons from the host to the external circuit during the charging and discharging processes are required. The electrochemical performance of an electrode material, however, depends on several aspects, varying from the composition, structure, to the morphology of the secondary and primary particles that constitute the active electrode material.